US President Barack Obama for the first time Wednesday invoked executive privilege to withhold documents from a congressional investigation into a botched US gun-smuggling probe that Republicans have used to attack his administration as the November election approaches.

The decision came as a House of Representatives committee was poised to vote on whether to hold Attorney General Eric Holder in contempt of Congress for failing to turn over more Justice Department files.

The committee wants documents that explain how the department learned of problems with the Operation Fast and Furious probe along the Mexican border. But Obama decided to withhold them.

The president has asserted executive privilege, Deputy Attorney General James Cole said in a letter to committee chairman Rep. Darrell Issa.

As the committees hearing began,Issa called the presidents action an untimely assertion of the privilege,which the White House says presidents have asserted just 25 times since 1980.

Republicans have suggested that the administrations failure to produce the documents suggests it is hiding embarrassing details.

In Fast and Furious,federal agents from the US Bureau of Alcohol,Tobacco,Firearms and Explosives in Arizona abandoned the agencys practice of intercepting all arms they believed to be illicitly purchased. Instead,the goal was to track such weapons to high-level arms traffickers,who had long eluded prosecution,and to dismantle their networks.